Postpartum thyroid dysfunction in pregnant thyroid peroxidase antibody-positive women living in an area with mild to moderate iodine deficiency: Is iodine supplementation safe?

In moderately iodine-deficient, pregnant, thyroid peroxidase antibody (TPO- Ab)-positive women the role of iodine supplementation in the development of postpartum thyroid dysfunction (PPTD) was studied in a placebo-controlled, randomized, double blind trial. Screening for TPO-Ab was performed in earl y pregnancy in a population of healthy pregnant Danish women with no previo us diagnosed thyroid disease (prevalence, 117 of 1284; 9.1%). The participa nts were randomized, stratified according to TPO-Ab, level, to three groups . All participants received a daily vitamin and mineral tablet with 150 mu g iodine or no iodine. The +/+ group received iodine during pregnancy and t he postpartum period, the +/- group received iodine during pregnancy only, and the -/- group received no iodine supplementation. A total of 66 TPO-Ab positive women were followed, and in the postpartum period sera were collec ted at 8-week interval for biochemical evaluation of thyroid function and a ntibody level. Compliance was evaluated by 24-h urinary iodine measurements . PPTD developed in 55% of the participants. In 67% of the cases abnormal TSH was accompanied by abnormalities in thyroid hormones, whereas 33% had abno rmal serum TSH only. There was no statistically significant difference in t he frequency of PPTD in the three groups: +/+ group, 59% (95% confidence in terval, 36-79%); +/- group, 60% (36-81%); and -/- group, 46% (26-67%). Ther e were also no differences in the severity of the PPTD, as evaluated by dur ation and grade of deviation of TSH and thyroid hormones from normality. Th e occurrence, severity, and type of PPTD predominantly depended on the TPO- Ab level: TPO-Ab below 200 U/L at screening, 35% developed PPTD; TPO-Ab of 200-900 U/L, 54%; and TPO-Ab above 900 U/L, 75% developed PPTD. Women with low levels of antibodies predominantly remained euthyroid or had hyperthyro idism only, whereas women with high antibody levels had hyperthyroidism fol lowed by hypothyroidism or hypothyroidism only. We conclude that iodine sup plementation (150 mu g) during pregnancy and the postpartum period to TPO-A b-positive women living in an area with mild to moderate iodine deficiency did not induce or worsen PPTD. The study confirmed that screening for TPO-A b in early pregnancy can predict women at high risk for development of PPTD .